Ambulatory electrocardiographic patient monitoring system and method therefor

ABSTRACT

An ambulatory patient monitoring system (100) is provided for measuring and storing predetermined diagnostic parameters of a patient. The monitoring system includes a personal type computer (120) which may be selectively coupled to the portable portion (102) of system (100). Portable portion (102) may include one or more monitoring modules, such as ECG monitoring unit (110) and blood pressure monitoring unit (210). When ECG monitoring unit (110) and blood pressure monitoring unit (210) are disposed in side-by-side relationship and with respective optical interfaces (50, 254) in optical alignment, the two units operate in concert. ECG monitoring unit (110) supplies an R-wave gating signal to blood pressure monitoring unit (210) for establishing a window in which the receipt of a Korotkoff sound is expected. Additionally, the ECG unit (110) may trigger the blood pressure unit (210) to take a reading responsive to unit (110) identifying a predetermined abnormality in the ECG signal. Alternately, ECG monitoring unit (110) and blood pressure monitoring unit (210) may be used independently of one another as separate monitoring devices.

REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a divisional patent application of a U.S.Pat. application Ser. No. 07/790,500 filed on 12 Nov. 1991, now U.S.Pat. No. 5,238,001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention directs itself to ambulatory monitoring systems formeasuring and storing diagnostic parameters. In particular, thisinvention directs itself to a modular monitoring system, wherein modularmonitoring units can be used either independently of one another, orutilized together with at least one module communicating to anotherthrough an optical interface. More in particular, this invention directsitself to a system wherein the patient's ECG waveform is monitored andanalyzed to identify particular abnormalities, both the ECG waveform andanalysis data being stored in a non-volatile memory. Further, thissystem is directed to a blood pressure monitoring module for takingmeasurements responsive to a selectively variable repetition rate,selectively actuated for predetermined time intervals, and at timestriggered by the ECG monitoring unit, when both are being utilized. Morein particular, this invention pertains to an ambulatory monitoringsystem wherein each of the monitoring unit modules includes a serialinterface for coupling with a personal-type computer to allow thephysician to program predetermined parameters, observe measurements inreal time, and download measurement data stored in the memory of each ofthe modules. Further, this invention directs itself to ambulatorymonitoring units having means for conserving power to enable the unitsto operate for over twenty-four hours on battery power. Such powerconserving means may take the form of a system to vary the operationalspeed of the monitoring unit's microprocessor, or alternately shuttingdown the operation of the unit's microprocessor for predeterminedperiods of time.

2. Prior Art

Some prior art systems, such as that disclosed in U.S. Pat. Nos.4,211,238; 4,216,779; and, 4,519,398 are directed to ambulatorymonitoring systems for both blood pressure and a patient's ECG. In suchsystems the ECG signal is continuously monitored and stored in a memoryor on a magnetic tape. The blood pressure measurement may be made atparticular time intervals, with only a provision for manually initiatinga measurement at intermediate times. Such blood pressure measurementsare stored with the continuous ECG signal, however, there is noprovision for the ECG unit triggering a blood pressure measurement.

In other prior systems, such as that disclosed in U.S. Pat. No.4,566,463 automatic blood pressure monitoring systems are disclosedwhich are capable of operating responsive to heartbeat abnormalities.While such systems attempt to detect arrhythmias and generate a controlsignal for initiating the blood pressure measurement, such systemsutilize pressure pulse from the blood pressure cuff as the means todetect arrythmias. Further, these systems are not of modularconstruction wherein the communication between modules is devoid ofcabling, and the problems associated therewith. Still further, suchsystems lack means for conserving power, which is essential in portablelong-term monitoring systems.

SUMMARY OF THE INVENTION

An ambulatory patient monitoring system is provided for measuring andstoring predetermined diagnostic parameters of a patient. The ambulatorypatient monitoring system includes a first monitoring unit forindependently measuring and storing a predetermined first diagnosticparameter of a first patient responsive to a first control algorithm.The first monitoring unit includes a first optical interface circuit fordigital communication. The first monitoring unit further includes afirst memory circuit for storing the first diagnostic parameterstherein. The ambulatory patient monitoring system further includes atleast a second monitoring unit for measuring a predetermined seconddiagnostic characteristic responsive to a first control signal, andstoring the second diagnostic parameter responsive to a second controlalgorithm. The first control signal is generated at a selectivelyvariable repetition rate, selectively actuated for predetermined timeintervals. The second monitoring unit includes a second opticalinterface circuit for digital communication with at least the firstmonitoring unit. The second monitoring unit is (1) independentlyoperable for measuring the second diagnostic characteristic of a secondpatient, the second diagnostic characteristic being different than thefirst diagnostic characteristic, and (2) positionable in opticalalignment with the first monitoring unit for measuring the seconddiagnostic characteristic of the first patient responsive to both thefirst control signal and a second control signal. The second controlsignal being generated by the first monitoring unit and transmitted bythe first optical interface circuit to the second optical interfacecircuit. The second monitoring unit also includes a second memorycircuit for storing the second diagnostic characteristics therein. Theambulatory patient monitoring system further includes a computing systemselectively coupleable to both the first and second monitoring units fortransferring data therebetween and selectively displaying the first andsecond diagnostic characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the ambulatory monitoring system of thepresent invention in use;

FIG. 2 is a perspective view of the ambulatory monitoring system;

FIG. 3 is a perspective view of an alternate embodiment for the presentinvention;

FIG. 4 is a block diagram of the ECG monitoring unit;

FIG. 5 is a block diagram of the ECG analog signal conditioning circuit;

FIG. 6 is a block diagram of the pacemaker pacing spike detector;

FIG. 7 is a simplified logic flow diagram of the ECG analysis;

FIG. 8 is a circuit diagram of the ECG optical interface;

FIG. 9 is a block diagram of the blood pressure monitoring unit;

FIG. 10 is a block diagram of the K sound signal conditioning circuit;

FIG. 11 is a simplified logic flow diagram for the blood pressuremonitoring unit; and,

FIG. 12 is a simplified logic flow diagram of the rapid blood pressuremeasurement method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the Figures, there is shown ambulatory patient monitoringsystem 100 for measuring and storing predetermined diagnostic parametersof a patient. As will be seen in following paragraphs, ambulatorymonitoring system 100 is directed to the concept of providingsimultaneous ambulatory measurements of multiple diagnostic parameters,such as the electrocardiogram, blood pressure, oxygen saturation,temperature, and respiratory function, while still maintaining thecapability of utilizing the measuring devices for each of the diagnosticparameters independently, on different individual patients. Although notrestricted to the simultaneous measurements of the electrocardiogram andblood pressure, system 100 is particularly adapted to provide eventtriggered blood pressure measurements, the programmed blood pressuremeasurement protocol being interrupted in response to the detection of aparticular ECG abnormality identified by the ECG monitoring unit 110.Additionally, the blood pressure monitoring unit 210 is further enhancedthrough the use of an R-wave gating signal, for use in the auscultatorymethod of blood pressure measurement transmitted from the ECG unit 110to the blood pressure monitoring unit 210, the blood pressure unit 210using the gating signal to establish a window for detecting of Korotkoffsounds (K sounds), thereby reducing the likelihood of detectingtransient noise, motion artifacts, or the like as valid K sounds.Further, unit 210 is capable of measuring blood pressure in anoscillometric mode, using pressure pulsations in the cuff to establishthe systolic and diastolic levels. The oscillometric method can becarried out substantially simultaneously, with both sets of measurementsstored for subsequent comparison, however, there is currently noclinical need for both sets of data. Therefore, unit 210 switches to theoscillometric method when K sounds cannot be detected, acting as a failsafe. If the cuff pressure drops below a predetermined value and Ksounds have not yet been detected, the cuff is reinflated and thedeflation process repeated using the oscillometric method.

Ambulatory monitoring system 100 is modular in construction to provideat least three monitoring systems in one, and having the capacity togreatly exceed that number. In the configuration shown in FIG. 1, theportable portion 102 of system 100 provides for the simultaneous andcoordinated measurement of both ECG and blood pressure parameters,functioning as a single instrument. Additionally, each of the monitoringunits 110, 210 may be used individually, each unit being useable on adifferent patient. Hence, system 100 can be configured as threedifferent instruments, two of which being operable simultaneously.

In the exemplary configuration shown in the Figures, the ECG monitoringunit 110 functions as the master unit, with the blood pressure unit 210defining a slave unit. As a slave unit, and in addition to makingmeasurements in accordance with a programmed protocol, the bloodpressure unit is responsive to predetermined events identified by themaster ECG monitoring unit 110 for initiating a blood pressuremeasurement. In addition to the ECG and blood pressure monitoring units,system 100 may incorporate other modular ambulatory monitoring units foruse with either or both of the ECG and blood pressure units, such as formonitoring oxygen saturation, temperature, electroencephalographsignals, one or more respiratory functions, and myoelectric potentialsfrom particular portions of the patient's body. Each of these modulesmay be utilized independently, or placed in various combinations to forma monitoring instrument tailored to suit the diagnostic requirements fora particular patient. For instance, an oxygen saturation measuringmodule could be used in combination with both units 110 and 210, or usedwith either one, alone. Such an oxygen saturation measurement modulecould function as a master unit, triggering blood pressure measurements,or as a slave, being triggered by the ECG unit 110. Further, system 100may include a telemetric module, for transmitting data measurements,either in real time, or downloaded from a respective module's memory,for transmission to a remote receiver through an optical orradiofrequency data link.

Referring now to FIG. 1, there is shown the portable portion 102 ofambulatory monitoring system 100 as might be worn by a patient. The ECGmonitoring unit 110 and the blood pressure monitoring unit 210 aredisposed in side-by-side relationship within a carrying pouch 104, andreleasably secured to the patient by means of a belt or strap 106. Theexact form or means for releasably securing the portable portion 102 ofsystem 100 is not important to the inventive concept, and may beaccomplished by any of a number of harness or strap arrangements, wellknown in the art. It should be noted that units 110 and 210 need not bedisposed in abutting relationship, as it is only necessary that theirrespective optical communication interfaces be aligned, one with respectto the other. A plurality of ECG electrodes 114, each having arespective lead 112 of a multiple lead cable 108 defining ECG leadpairs, are part of an ECG electrode assembly 109, coupled to the ECGmonitoring unit 110. Electrode assembly 109 further includes a referenceelectrode 115 coupled to a lead 113. ECG electrodes 114 and 115 may beany of a wide variety of disposable or reusable electrodes, well knownin the art.

The blood pressure monitoring unit 210 includes an inflatable cuff 204which carries an audio transducer 206, positioned adjacent the patient'sarm, for converting the K sounds to electrical signals transmitted tomonitoring unit 210 through an electrical cable 208. The cuff 204 isinflated and deflated through a hose 202 coupled to a fluid pump orcompressed fluid supply and a bleed valve. The transducer cable 208 maybe integrated into the hose 202, wherein cable 208 is coupled to anexterior surface of hose 202, extends through the fluid carrying lumen,or through a separate lumen formed therein.

Referring now to FIG. 2, there is shown ambulatory patient monitoringsystem 100 wherein a personal-type computer 120 is coupled to respectivediagnostic parameter measuring units 110, 210, by means of opticallyisolated serial data links 124, 224. Bidirectional communication betweenthe monitoring units 110, 210 and the personal-type computer 120 isprovided through respective serial interfaces 48, 252 (shown in FIGS. 4and 9) which are coupled to respective serial ports of computer 120through respective connectors 118, 218 and serial data cables 124, 224.The physician utilizes the personal-type computer 120 to enterparticular patient information, which is relevant to identifying thatpatient and the data collected therefrom, as well as enter particularmeasurement protocols, operating parameters, and event triggering data,to be more fully described in following paragraphs. Thus, the computer120 allows the physician to program particular functions of themonitoring units 110, 210 for tailoring the diagnostic measurements to aparticular patient.

The computer 120 further serves as a means for retrieving data from therespective monitoring units 110, 210. Each of units 110, 210 areprovided with sufficient memory for storing the diagnostic parametersmeasured over at least a twenty-four hour period. Thus, all of themeasurement data stored within a respective measuring unit 110, 210 canbe downloaded to the main memory and mass storage systems of computer120 through the serial data connections selectively establishedtherebetween. Additionally, the measurement data can be transmitted tocomputer 120 in real time, as the measurements are being taken. In thisreal time data mode, the measurements can be displayed on the computer'smonitor, that is, both the ECG waveforms, heart rate and blood pressuremeasurements can simultaneously be displayed. Additionally, the K soundscan be displayed and converted back to an audio signal for dynamicallychecking the blood pressure measurement data, further signal analysisand facilitating blood pressure measurement algorithm development.Computer 120 includes a digital to analog converter coupled to a speaker136 through an audio cable 134, for playing back the K sounds while thecuff pressure measurements are displayed on the computer's monitor.

Subsequent to the stored data being downloaded, the physician candisplay for any time period, the ECG waveform, the heart rate, as wellas display the number and time of day of the occurrence of abnormalconditions. Such abnormal conditions as arrhythmias, absence ofparticular ECG waveform components, and pacemaker malfunctions areseparately identified and classified. Arrhythmias are further identifiedand classified as to type, such as ventricular tachycardia, paroxysmalsupraventricular tachycardia, bradycardia, dropped beats or pauses,couplets, runs, for example. Of particular importance is the fact thatECG monitoring unit identifies these abnormal conditions as they occur,and can be programmed to trigger a concurrent blood pressure measurementconcurrently therewith.

Referring now to FIG. 3, there is shown an advantage of the opticalinterface 50, 254 for units 110, 210, respectively, in combination withthe real time mode of the units. The patient may be provided with amodem 130 and an optical interface unit 122, coupled to modem 130 bymeans of a serial data cable 128 for communicating with the ECGmonitoring unit 110. ECG unit 110 is being described with respect toFIG. 3 for exemplary purposes, it should be understood that bloodpressure monitoring unit 210, or any other module of system 100, can besubstituted interchangeably for unit 110, as this portion of the systemoperation applies equally to any of the monitoring units.

Optical interface unit 122 includes an optically transmissive window126, which complements the window 116 of the monitoring unit 110, and isprovided with similar circuitry to permit optically isolatedcommunication through the telephone line 132, to the physician'spersonal-type computer 120, or some other computing system or digitalequipment. In this fashion the physician can monitor the patient's ECGwaveform remotely, or alternately download the data stored within thememory of the ECG monitoring unit 110 for monitoring the data previouslyobtained.

Turning now to FIG. 4, there is shown a block diagram for the ECGmonitoring unit 110. The ECG electrode cable 108 carries signals fromtwo pairs of electrodes 114, defining two ECG channels. The leadsrepresenting these two ECG channels are carried by the cable 108 and arecoupled to an impedance switching network 10. Impedance switchingnetwork defines a digitally controlled switch capable of injecting asmall test current back through the leads to the patient. This testcurrent establishes a voltage across a respective pair of leads which isused to measure the impedance across the electrodes, thereby allowingthe physician to insure proper electrode coupling with the patient. Theimpedance checking function carried out through the switch network 10 iscontrolled through the coupling line 11 which couples switch network 10to microprocessor 30. The ECG signal amplification circuits,analog-to-digital converter, and microprocessor are utilized in thisimpedance measurement. Thus, the electrical signals conducted from theelectrodes of the respective channels, either the substantially constantvoltage of the impedance measurement or the ECG waveform signals, arecoupled to respective signal conditioning circuits 12, 18 by means ofrespective coupling lines 7, 9.

As shown in FIG. 5, the signal conditioning circuit 12 comprises a fixedgain amplifier 300 having an input coupled to the coupling line 7, andan output coupled to a high pass filter circuit 302. High pass filtercircuit 302 has a lower cut-off frequency approximating 0.05 hertz, andmay be constructed as either an active or passive filter circuit,however, an active filter circuit is preferred. The output of high passfilter 302 is coupled to the input of a variable gain amplifier stage304. Variable gain amplifier stage 304 is digitally programmable, havinga gain control digital link 13 coupled to microprocessor 30. Thevariable gain of amplifier 304 stage may be adjustable within a range of0.5-21, and preferably within a range of 3 to 12.5. Variable gainamplifier stage 304 may further include a fixed gain amplifier incombination therewith. The output of variable gain amplifying stage 304is coupled to a low pass filter 306, having a frequency cut-off ofapproximately 40 hertz.

The gain of variable gain amplifier stage 304 is adjusted bymicroprocessor 30 by sampling the ECG signals with the gain set at aminimum value. If the peak amplitude of the detected R-wave is less thana predetermined value, the gain is increased by an incremental value. Ifat this increased gain step the R-wave amplitude is less than a secondpredetermined value, the gain is advanced another step, otherwise itwill remain. Although three incremental levels of gain have provedsatisfactory, obviously, more or less increments of gain could beemployed without departing from the spirit and scope of the invention.

Since the second ECG channel signal conditioning circuit 18 is identicalto that of circuit 12, such has not been shown. The variable gainportion of the signal conditioning circuit 18 is controlled through adigital link 15 coupled to microprocessor 30, as shown in FIG. 1, toprovide independent and variable gain for that respective channel. Theoutput 14, 20 of each of the signal conditioning circuits 12 and 18 arerespectively coupled to an analog-to-digital multiplexing converter 16by means of the respective coupling lines 14 and 20. In addition to therespective output lines 14, 20 of the signal conditioning circuits 12,18, the output of a battery monitoring circuit 17 is coupled to oneinput of the multiplexing A-to-D converter 16 for providing batterycondition data to microprocessor 30. When microprocessor 30 detects thelow battery signal, it stores the alarm condition and the time of daythat it occurred, which is recovered when the physician down loads thememory. An alarm indication could be triggered in response to a lowbattery condition to alert the patient, but the consequences of notdoing so is simply to repeat the test, and therefore provides littlejustification for inclusion of the feature. Multiplexing A-to-Dconverter 16 sequentially converts the analog signals on each of theinput lines to a multi-bit digital representation thereof, forcommunication to microprocessor 30 through the coupling line 26. Onemultiplexing analog-to-digital converter successfully utilized in system100 is a 12-bit device having the designation TLC1540, manufactured byTexas Instruments, Inc. of Dallas, Tex.

The ECG monitoring unit 110 includes a pacemaker spike detector circuit24 having an input coupled to the output line 20 of the channel 2 signalconditioning circuit 18. As shown in FIG. 6, the pacemaker spikedetector circuit 24 includes a high pass filter circuit 308 having aninput coupled to line 22. High pass filter 308 is provided with afrequency cutoff at 20 Hertz to remove the ECG signal and any muscleartifacts which might be present in the signal. The output of high passfilter 308 is coupled to an absolute value amplifier 310. An absolutevalue amplifier is utilized because the pacemaker spike may be either apositive or negative going pulse, which otherwise would require separateamplification and detection stages, the outputs of which would then haveto be combined. Absolute amplifier 310 has a gain value approximating500 for amplifying the pacemaker spike signal to a magnitude within therange of 10 through 500 millivolts. The output of absolute valueamplifier 310 is coupled to the input of a peak detector 312. Peakdetector 312 establishes a threshold value which must be exceeded for adigital logic level signal to be output on line 25 for coupling withmicroprocessor 30. Peak detector 312 is a conventional comparator-typecircuit arrangement, well known in the art, with a threshold valueapproximating 15 millivolts. The pulse provided to microprocessor 30through coupling line 25 is subsequently analyzed to determine if thesignal provided on line 25 is in fact a signal representing thepacemaker spike. A pacer signal from a pacemaker has a fixed pulsewidth, typically in a range between 0.5 and 2.0 milliseconds, themicroprocessor 30 therefore disregards any signal supplied by pacemakerspike detector circuit 24 which is outside that range. Thus, data may beaccumulated on the operation of a patient's pacemaker. This feature isparticulary advantageous for a patient having the type of pacemaker witha pacing rate which is variable responsive to the patient's activitylevel.

Microprocessor 30 is a multipurpose processing device which performscommunication and analytical functions of monitoring unit 110. In oneworking embodiment, microprocessor 30 is a commercially available 16-bitsingle chip microprocessor having a designation 68332, available fromMotorola Semiconductor, Inc. of Phoenix, Ariz. The ECG data suppliedthrough line 26 from the analog-to-digital converter 16 is monitored todetermine whether the gain is properly set in the respective signalconditioning circuits 12 and 18, the microprocessor outputting controlsignals on respective control lines 13, 15 for selecting the appropriategain values for input to the signal conditioning circuits 12, 18.Microprocessor 30 further performs real-time analysis of the ECG data,which along with the raw ECG data is processed through a datacompression algorithm, and stored in the electrically erasable,electrically programmable read-only memory 46. Memory 46 is constructedfrom commercially available memory devices known as Flash memorydevices, having a manufacturer's designation 28F020, available fromIntel Corporation of Santa Clara, Calif. Data storage memory 46 provides4 megabytes of non-volatile memory for storage of the ECG and analysisdata within monitoring unit 110.

Referring now to FIG. 7, there is shown, a simplified flow diagram ofthe ECG data processing steps carried out by microprocessor 30. Thedigitized data representing the ECG signal from either one of the twoinput channels (each of the channels being processed alternately) isprovided from the input block 150 to the smoothing filter block 152. Thesmoothing filter step represented by block 152 utilizes well knowntechniques for enhancing the signal, with respect to noise. The smootheddata is supplied to the data compression block 166, wherein a data bitreduction procedure is carried out. The compressed data from block 166is provided to the storage output block 168, providing the data forstorage within the data storage memory 46, followed by the step ofreducing the frequency of clock circuit 32, in block 167. The importanceof changing the clock frequency will be described in followingparagraphs.

The filtered data from block 152 is also supplied to the beat detectiondecision block 154. When a beat is detected, the data is transmittedfrom decision block 154 to the beat classification block 156 and theheart rate computation block 164. The heart rate computed in block 164is transmitted to data compression block 166 for subsequent storage inthe data storage memory 46. Classification block 156 identifiesarrhythmias from the beat timing supplied from the beat detection block154, classifying the beat into predetermined categories. The arrhythmiatype identified by the beat classification block 156 is transmitted tothe data compression block 166 for storage in the data storage memory46. Additionally, the arrythmia type is transmitted to the rhythmclassification block 162 so as to further distinguish reoccurring eventsfrom those of a transient nature. The output of rhythm classificationblock 162 is similarly transmitted to the data compression block 166 forstorage in data storage memory 46. The output of the beat classificationblock 162 is also supplied to the blood pressure trigger detectiondecision block 158, and if the type of arrhythmia or rhythm identifiedby block 162 matches that which has been predetermined to require asimultaneous blood pressure measurement, previously entered by thephysician, then the signal transmission output block 160 is enabled, forsending a trigger control signal to the blood pressure unit through theoptical data link, as has previously been described.

Referring additionally to FIG. 4, microprocessor 30 is coupled to aclock circuit 32, which may be provided internal to microprocessor 30 oras an ancillary device. Clock circuit 32 provides the basic clockimpulses, whose frequency determines the operational speed at whichmicroprocessor 30 operates. The clock signals output from clock circuit32 are supplied to microprocessor 30 through coupling line 34, as isconventionally found in microprocessor systems. However, microprocessor30 includes an output line 32 coupled to clock circuit 32 forcontrolling the clock frequency supplied therefrom.

As is well known in the art, complementary metal oxide microprocessordevices consume power in direct relation to their operating speed, thusit is possible to reduce the power consumption of microprocessor 30 bymaintaining a low clock frequency. This however, would have adetrimental effect on performing data compression and arrhythmiaanalysis in real time. To achieve the advantages of a reduced clockfrequency, while obviating the disadvantage such would have onprocessing intensive functions, the clock speed control output 32 isutilized to adapt the clock circuit frequency to the function beingperformed by the microprocessor. Thus, responsive to detection of heartbeats in decision block 154, the frequency of clock 32 is increased tosupport the real time processing of the ECG data. It should beunderstood that the frequency reduction step of block 169 is not reacheduntil all of the data, raw and analysis, has been stored.

Thus, for high powered processing (significant computation), the clockcircuit is operated at its highest frequency, 8 megahertz for example,and during periods, between heartbeat signals, the clock frequency maybe reduced down to its lowest operating frequency, such as 32 kilohertz,or some frequency in between those limits, as a function of the type ofprocessing which is to be performed. Use of this adaptable clockfrequency saves considerable power in ECG monitoring system 110. Thispower saving feature is of critical importance for a portable systemoperating from a battery power supply, which must function continuouslyand reliably for over a 24-hour period. Minimization of power supplysize substantially contributes to minimization of unit 110, whichprovides particular advantages for a device that must be worn by apatient for extended periods of time.

As previously described, microprocessor 30 provides output data which isstored in the programmable read-only memory 46, through the data bus 38with appropriate addressing supplied through the address bus 37.Microprocessor 30 is further supported by 128-kilobytes of random accessmemory 42 as temporary storage for use in the data compression andarrhythmia analysis processing. The operations of microprocessor 30 arecontrolled by a program stored in program memory 44, coupled to the databus 38 and address bus 37. Program memory 44 is a 256-kilobit read-onlytype memory. Read-only type memory 44 may be constructed of the Flashtype memory devices, similar to those utilized in memory 46, therebyallowing field upgrades of the control program software for ECGmonitoring unit 110 utilizing the electrical erasure and programmingfunctions of the device. In this manner, each of the memory subsystems42, 44 and 46 are each coupled to data bus 38 and address bus 37. Alsocoupled to data bus 38 is a general I/O interface 36 which is selectedby means of the I/O port selection control line 39, coupled tomicroprocessor 30. The input to general interface 36 is coupled to amomentary push-button switch 35 for coupling a reference potentialthereto. Switch 35 functions as an event switch, which functions as anevent marker for the ECG signal. Thus, if the patient finds himself outof breath, or lightheaded for example, he can mark the occasionutilizing the event switch. An indication that the event switch wasoperated will be stored along with the ECG data currently beingmeasured. General interface 36 may comprise a commercially available74HCT540 tristate buffer line driver, available from MotorolaSemiconductor Products, Inc. of Phoenix, Ariz.

As previously described, ECG monitoring unit 110 includes a serialinterface connector 118 for coupling with an external computing device.Connector 118 is coupled to serial interface 48 by means of a respectiveserial input and output line, the serial interface being coupled in turnwith microprocessor 30 by means of respective input and output lines 43and 45. Serial interface 48 may be incorporated into microprocessor 30,or constructed from any one of a plurality of commercially availableserial interface circuits for coupling with microprocessor 30.Similarly, the optical interface 50 is coupled to microprocessor 30 bymeans of respective input and output lines 40 and 41. The opticalinterface 50 converts electrical signals transmitted from microprocessor30 into optical signals, preferably within the infrared bandwith of theelectromagnetic spectrum, which are transmitted through the transmissivewindow 116 to a slave module, such as the blood pressure measuring unit210. Optical signals from the slave module pass through transmissivewindow 116 and are received by an optical detector, such as aphototransistor, for conversion to electrical signals which aretransmitted to microprocessor 30 by line 40.

Referring now to FIG. 8, there is shown the optical communicationsinterface 50 coupled to microprocessor 30. Optical interface 50 includesthree light emitting diodes 70, 72 and 74, each coupled in series with arespective current-limiting resistor 76, 78 and 80. Each of resistors76, 78 and 80 being coupled to a common power supply terminal 82 forreceiving the positive power supply voltage thereon. The opposing end oflight emitting diodes 70, 72 and 74 being coupled to the output of arespective tristate buffer amplifier 84, 86 and 88. The use of tristatebuffers for driving the light emitting diodes 70, 72 and 74 is anotherpower-saving feature incorporated into ECG monitoring unit 110.

The light emitting diodes are turned off when the interface is disabled,by means of the interface enable control line 92 coupling microprocessor30 to each of the tristate control inputs 83, 85 and 87 of therespective tristate amplifiers 84, 86 and 88 coupled to light emittingdiodes 70, 72 and 74. Thus, when the drivers are placed in the highimpedance mode, disabling the interface, no power is consumed by thelight emitting diodes. This would otherwise not be the case, since thestate of some of the peripheral lines, such as the clock line 98 cannotbe controlled and thus, would otherwise permit the light emitting diodesto consume power.

When microprocessor 30 outputs a logic low level signal on line 92, eachof the drivers 84, 86 and 88 is enabled, turning light emitting diode 70on, allowing transmission of serial data from line 96 through the lightemitting diode 72, and transmission of the serial clock from line 98through light emitting diode 74. Serial data is received from the slavemodule, such as the blood pressure monitoring unit 210, through thephototransistor 73. Phototransistor 73 is coupled in series with a loadresistor 75, which is in turn coupled to the positive power supply inputterminal 82. The emitter of the phototransistor 73 is coupled to theground reference potential for the system. The output of phototransistor73, taken from the collector thereof, is coupled directly tomicroprocessor 30 on interrupt line 95.

The presence of a signal on interrupt line 95 alerts the microprocessorto the transmission of data from the slave module, in order to interruptits current processing operation and direct appropriate resources to thereceipt of the incoming data. Additionally, the output ofphototransistor 73 is coupled to the input of the tristate bufferamplifier 90 for transmission through the serial input line 94 tomicroprocessor 30. As with the other tristate buffer amplifiers,amplifier 90 includes a tristate control input 91 which is coupled tothe interface enable control line 92. When the slave module initiates anoptical transmission to ECG unit 110, the received signal changes thelogic state of interrupt line 95 from a high to a low level, generatingthe interrupt signal internal the microprocessor 30. Microprocessor 30responds by changing the logic level of the interface enable line 92from a high to a low, illuminating light emitting diode 70 to indicateto the slave module that microprocessor 30 is ready to receive data, thedata being synchronized with the serial clock signal of microprocessor30, transmitted by light emitting diode 74. With respect to the blockdiagram of FIG. 4, output lines 92, 96 and 98 are represented bycoupling line 41, and input lines 94 and 95 are represented by couplingline 40.

Each of units 110 and 210 are capable of using their respective opticalinterface to automatically detect the presence of the other respectiveunit. When unit 110, for instance, is turned on and completes initialself test and calibration functions, a signal is transmitted by theoptical interface 50. If after a predetermined delay no response isreceived, ECG unit 110 operates as an independent unit, unless aninterrupt signal is received on line 95 at some later time. In thismanner ECG unit 110 can save power, by not transmitting an R-wave gatingsignal for every beat. Similarly, the blood pressure unit 210 is capableof detecting the presence of the ECG unit, for determining whether it isto function as an independent unit. However, the operational mode ofunit 210 could be set at the time the measurement protocol is programmedby the physician.

Referring now to FIG. 9, there is shown a block diagram of the bloodpressure monitoring unit 210. A transducer assembly 214 includes anaudio transducer 206, which may be a microphone, for converting the Ksounds into electrical signals transmitted by electrical cable 208 tosignal conditioning circuit 270, which performs amplification andfiltering functions, to be described in following paragraphs. The outputof signal conditioning circuit 270 is coupled to analog-to-digitalmultiplexing converter 266 through coupling line 268. Coupling line 268represents the output of several signals from signal conditioningcircuit 270, to be more fully described in following paragraphs. Thedigitized output of the analog-to-digital multiplexing converter 266 issupplied to microprocessor 262 through coupling line 264. Microprocessor262 provides a control signal to signal conditioning circuit 270 bymeans of coupling line 271 for controlling the amplification gainthereof,

The transducer or sensor assembly 214 further includes a pressuretransducer 212 for measuring the inflation pressure of cuff 204 throughhose 202. The electrical output of pressure transducer 212 is coupled toamplifier 274 through coupling line 232. The output of amplifier 274 iscoupled to analog-to-digital multiplexing converter 266 through couplingline 272. As in the ECG monitoring unit 110, blood pressure monitoringunit 210 includes a battery monitoring circuit 248 having an outputcoupled to an analog-to-digital multiplexing converter 266 throughcoupling line 249. Microprocessor 262 stores the alarm condition andtime of day it occurred with the blood pressure data. Thus, the multipleoutputs derived from the audio transducer, the output from the pressuretransducer, and the output of the battery monitor are sequentiallydigitized and transmitted to microprocessor 262. Analog-to-digitalmultiplexing converter is a commercially available device, like thatutilized in monitoring unit 110, previously described.

Microprocessor 262 may be an 8-bit microprocessor having internal serialinterface circuitry. One such microprocessor which has been successfullyutilized in this application has an identification number of 68HC811,from Motorola Semiconductor Products, Inc. of Phoenix, Ariz.Microprocessor 262 outputs a pump control signal on line 240 which iscoupled to a driver amplifier 242. The output of the driver amplifier242 is coupled to the pump 244 by means of the coupling line 243. Pump244 pumps fluid through an output conduit 245 through bleed valve 246and conduit 236 to pressure transducer 212, for coupling with cuff 204through hose 202. In particular, the fluid utilized is air, althoughother fluids may be substituted. As an alternative, pump 244 may bereplaced by an electrically actuated valve coupled to a supply ofcompressed fluid, which may be utilized to inflate cuff 204.

Transducer assembly 214 is utilized during the inflation step of theblood pressure measurement to determine when the patient's brachialartery has been occluded by the cuff, the pressure being over apredetermined value and there being an absence of K sounds. When theocclusion pressure is reached, pump 244 is shut down, by the change instate of the control signal output on line 240. Subsequently, a controlsignal is output on line 261 which is supplied to driver amplifier 260.Driver amplifier 260 provides an output on line 247 for controlling thebleed valve 246, which controls the release of fluid from cuff 204through hose 202 on conduit 236.

The rate at which fluid pressure is bled from the cuff 204 is controlledby the outlet orifice of bleed valve 246, with the increments ofpressure at which the microprocessor checks for the presence of K soundsbeing controlled by the length of time that the bleed valve is opened,that length of time being the time between beats. Thus, if the bleedrate were 2 millimeters of Hg per second, and the patient's heart ratewas 90 beats per second, the cuff pressure would decrease approximately1.3 mm of Hg. When the pressure is dropped, the microprocessor wouldcheck for detection of a K sound, and then proceed to open the bleedvalve for the next interval between beats. Each incremental pressurevalue is stored in memory during the measurement procedure. As inconventional blood pressure measurements, subsequent to the first Ksounds being detected, the reduction in pressure in cuff 204 continuesuntil there is an absence of K sounds. When R-wave gating is supplied bythe ECG monitoring unit 110, the microprocessor only looks at the outputof peak detector 336 a predetermined delay time after the R-wave signal.The pressure at which the K sounds cease to be detected establishes thediastolic pressure.

Referring now to FIG. 10, there is shown, a block diagram of the signalconditioning circuit 270. The electrical signals from audio transducer206 are supplied by line 208 to a variable gain amplifier stage 320. Thegain of amplifier 320 is controlled by a signal from microprocessor 262through the coupling line 271. The output of variable gain amplifier 320is coupled to a band pass filter 324 by means of line 322. Although notimportant to the inventive concept, band pass filter 324 may be anactive filter circuit having a center frequency approximating 23 hertz,low frequency cutoff approximating 11.5 hertz and an upper frequencycutoff approximating 34.5 hertz. The output of band pass filter 324 iscoupled to one channel of analog-to-digital multiplexing converter 266through coupling line 328, providing the K sound audio signals tomicroprocessor 262 for storage and subsequent analysis.

The provision for storing actual K sounds is a critically important newfeature for ambulatory blood pressure monitoring units. In conventionalsystems the physician manually takes a patient's blood pressure whilethe patient is at rest, comparing the manual measurement with theambulatory unit's measurement. Heretofore there has been no way for thephysician to check the ambulatory unit's calibration while the patientis active, when there is potential for greater inaccuracy due to motionartifacts. Since the actual K sounds are stored along with the pressuredata in memory, the physician can listen to the K sounds and observe thecuff pressure reading to establish his own blood pressure measurement,for comparison with which was determined by the measurement algorithm.Additionally, the stored K sounds can be input to more sophisticatedanalysis systems for further analysis. The stored K sounds facilitatethe development of new blood pressure measurement algorithms, providingan easy method for evaluating their accuracy over a wide range ofpatient activity.

Additionally, the output of band pass filter 324 is supplied to absolutevalue amplifier 330 through coupling line 326. Absolute value amplifier330 converts the bipolar audio signal output from filter 324 into aunipolar signal and outputs a signal representing the envelope thereof.The K sound envelope is coupled to a respective channel ofanalog-to-digital multiplexing converter 266 through coupling line 334.The output of absolute value amplifier 330 is also coupled to peakdetector 336 by means of coupling line 332. Peak detector 336 provides apulse output responsive to the K sound envelope signal exceeding apredetermined threshold, thereby providing a pulse indicating detectionof a K sound. The output of peak detector 336 is coupled to yet anotherchannel of analog-to-digital multiplexing converter 266 by means ofcoupling line 338. Each of the signal lines 328, 334 and 338 arerepresented by the signal line 268 in the block diagram of FIG. 9.

Referring back to FIG. 9, there is shown, a real time interruptgenerator 276 coupled to microprocessor 262 by means of the couplingline 277. Real time interrupt generator 276 forms part of a power savingsubsystem of blood pressure monitoring unit 210. Blood pressuremonitoring unit 210 is periodically put in a "sleep" mode wherein themicroprocessor operation is stopped and the current draw is dropped tothe microamp level, providing a substantial power savings. Subsequently,responsive to an output from real time interrupt generator 276 themicroprocessor is "awakened" to perform housekeeping chores, such asincrementing counters and checking status of communication ports, andtaking blood pressure measurements, as required.

Referring now to FIG. 11, there is shown, a simplified flow diagramrepresenting the cyclic operation of microprocessor 262. Responsive toan output from real time interrupt generator 276 a reset ofmicroprocessor 262 is initiated at block 172. The signal from real timeinterrupt generator 276 is a repetitive clock signal defining apredetermined increment of time, for example, 0.5 seconds. Thus,subsequent to initiation of the reset defined by block 172, the time ofday counter is incremented in block 174. The incremented counter ofblock 174 provides a time of day which is compared in block 176 with aselected measurement protocol to determine if it is time for a bloodpressure measurement to be taken. If a True condition results, then themicroprocessor's activity is controlled by the blood pressuremeasurement routine indicated by block 178. The measurement protocolwhich can be programmed by the physician is quite versatile. Inadditional to setting a repetition rate for the measurements, the ratecan be varied at different portions of the day. For instance, bloodpressure measurements may be scheduled to be taken every 10 minutes from7:00 to 9:00 A.M., every 30 minutes from 9:00 A.M. to 7:00 P.M., andevery 60 minutes from 7:01 P.M. to 6:59 A.M.

Subsequent to the measurement routine indicated in block 178 beingcompleted, or subsequent to the comparison step of block 176, where aNot True results, the microprocessor then tests, in block 180, whetherthe event switch has been operated. If the event switch has beenoperated then the microprocessor proceeds to perform a blood pressuremeasurement as indicated in block 182. If the event switch has not beenoperated, or subsequent to the blood pressure measurement having beenmade, the microprocessor checks the optical interface to determine ifthe ECG unit 110 is signalling that a blood pressure measurement shouldbe taken, so as to correspond to the occurrence of some predeterminedabnormality in the ECG signal. If such an event has occurred, then, asindicated in block 186, the microprocessor performs a rapid bloodpressure measurement, as will be more fully described in followingparagraphs. If the ECG has not triggered a blood pressure measurement,or such has been completed, the microprocessor then looks to the serialinterface 252 to determine if it is active, as indicated in block 188.If the result of this test is True, then the microprocessor performs thenecessary communications operations, as indicated in block 190. If thetest of block 188 is Not True, or such communications is completed, themicroprocessor is then put in a stop mode, as indicated by block 192,wherein its functions cease and power consumption is substantiallyreduced. This power saving feature is of critical importance to thedesign of monitoring unit 210, permitting continuous operation forgreater than 24 hours with a smaller size battery power supply thanwould otherwise be required. Such facilitates unit 210 being constructedas a small compact unit, which is particularly advantageous for a devicewhich must be worn by a patient for extended periods of time.

The event switch 235, shown in FIG. 9, is a momentary push-button switchcoupled in series with a load resistor 231 between the positive powersupply voltage, on one end of resistor 231, and the power supplyreference coupled to the opposing terminal of switch 235. Coupled to thenode between switch 235 and load resistor 231 there is provided an inputline 233 coupled to an input terminal of microprocessor 262. By thisarrangement, line 233 is held at a high logic level when switch 235 isopen, and brought to a low logic level when the contacts of switch 235are closed.

Optical interface 254, coupled to microprocessor 262, is constructed tocomplement that of optical interface 50 of the ECG monitoring unit 110.That is to say, that optical interface 254 is provided with a singlelight emitting diode for transmitting data from the blood pressure unit,and three phototransistors arranged to receive respective opticalsignals from each of the light emitting diodes 70, 72 and 74 of opticalinterface 50. The enabling signal transmitted by light emitting diode 70is received by a respective phototransistor in optical interface 254 fortransmission to microprocessor 262 through coupling line 239. Similarly,an optical signal transmitted from light emitting diode 74 of opticalinterface 50, through light transmissive window 216 of blood pressuremonitoring unit 210 is received by a respective phototransistor fortransmission of the clock signal to microprocessor 262 through line 259.The received clock signal being utilized for synchronization of theserial transmission sent to ECG monitoring unit 110 and the transmissionreceived therefrom. Thus, the serial data transmitted from lightemitting diode 72 of optical interface 50 is received by a respectivephototransistor within optical interface 254 and transmitted to theserial input of microprocessor 262 through line 257. The serial datatransmitted from microprocessor 262 is transmitted to optical interface254 by line 255, wherein a light emitting diode is driven to provide anoptical output transmitted through transmissive window 216 to ECGmonitoring unit 110 for receipt by phototransistor 73.

A serial interface 252 is provided for communication with such devicesas the personal type computer 120 shown in FIG. 1. The serial interfaceconnector 218 provides the means for coupling serial input and outputlines, through serial interface 252, to respective serial input andoutput ports of microprocessor 262. Serial data from microprocessor 262is carried by line 253 to serial interface 252, and serial datatherefrom is transmitted to microprocessor 262 by line 241.

Blood pressure measurements which are taken, in addition to the rawaudio signals, and the K sound envelope, are all stored in prgorammableread-only memory 256. Programmable read-only memory 256 is anelectrically erasable programmable read-only memory for providingnon-volatile storage of the blood pressure measurement data.Additionally, the software required to operate microprocessor 262 isstored within programmable read-only memory 256, along with the selectedmeasurement protocol entered by the physician through the personal typecomputer 120. Subsequently, the data is read from memory 256 andtransmitted through serial interface 252 for display, and possiblesubsequent processing by personal computer 120. Electrically erasableread-only memory 256 is formed by Flash memory devices, similar to thoseutilized in the ECG monitoring unit 110. One such Flash memory devicehas the part number designation 28F020, available from Intel Corporationof Santa Clara, Calif. Programmable ROM memory 256 is coupled tomicroprocessor 262 through the bidirectional data bus 250 and addressbus 251. Further, microprocessor 262 is coupled to 128 kilobit randomaccess memory 258 by means of bidirectional address bus 250 and addressbus 251. Random access memory 258 provides short-term storage for dataprocessing and a unique program storage function, to be furtherdescribed in following paragraphs.

Blood pressure monitoring unit 210 is provided in a very compact form,utilizing a minimum number of components, minimizing power consumption,and maximizing efficiency of those components utilized. By maintainingthe program storage within the same memory subsystem as is utilized fordata storage, storage density is maximized, as data may be storedbeginning with those memory locations immediately following thoseutilized for program storage. If subsequent software upgrades enlargethe size of the program storage requirements, the data storage is justsimply started at a higher address location. As long as the totalremaining programmable read-only memory is sufficient for a 24-hourperiod of data accumulation, the overall system performance will not beaffected. However, in such systems wherein the program memory isseparate from the data memory, excess storage capacity must be reservedfor future expansion, and future increases in storage requirements forprogram memory could necessitate hardware modifications to provideadditional storage, even though the data memory contains excess storagecapacity. This wastefulness, adding memory in one area while an excessof memory exists in another, is eliminated by storing the operatingprogram in the same non-volatile memory as the data. However, in orderto accommodate this virtual program memory storage, such eliminates theability to selectively erase only the data storage portion of memory256.

The solution to this latter problem is provided with the utilization ofthe random access memory 258. Prior to erasure of programmable read-onlymemory 256, the operating program for microprocessor 262 is transferredfrom read-only memory 256 to random access memory 258. Subsequent to thetransfer of the operating program, programmable read-only memory 256 iserased, to permit use on a new patient, or to gather another 24-houraccumulation of data on the same patient. While the oeprating program isstored in random access memory 258 such can be modified with newmeasurement protocols entered by the physician through serial interface252. Additionally, if the operating program is to be replaced, suchreplacement may be entered through interface 252 for storage inprogrammable read-only memory 256, subsequent to erasure thereof.

Referring now to FIG. 12, there is shown a flow diagram for the rapidblood pressure measurement selected to be utilized by the physician,responsive to particular transient abnormal conditions identified by theECG monitoring system 110. Responsive to the ECG monitoring unittriggering a blood pressure measurement at entry block 340, the pump 244is turned on, as indicated in block 342. Subsequent to the pump turn on,and after a predetermined delay to inflate the cuff to a predeterminedpressure, microprocessor 262 tests to see if K sounds are present, asindicated in block 344. If K sounds are present, such indicates that thebrachial artery is not occluded, and the inflation provided by theenergization of pump 244 continues until K sounds are no longerdetected. When K sounds are no longer detected, pump 244 is turned off,as indicated in block 346. Immediately thereafter, the bleed valve 246is deflated in predetermined, relatively large steps, in theapproximating range of 5.0-10.0 millimeters of Hg, indicated in block348. At each incremental drop in cuff pressure, microprocessor 262 teststo determine if any K sounds are present, as indicated in block 350. Ifno K sounds are found, the cuff 204 is deflated another increment, thisprocess continuing until K sounds are detected. When K sounds aredetected the pressure reading, as indicated by an output from thepressure transducer 212, is stored in memory, as indicated in block 352.By utilizing this rapid deflation of cuff 204 in order to establish acoarse approximation of the systolic blood pressure, a clinicallysignificant measurement is provided for determining whether ahypotensive condition has coincided with a transient condition ofelectrocardioactivity. If this approximation of systolic pressure wasbelow a predetermined minimum value, as a result of the arrhythmia, adiastolic measurement would not be indicated in the data.

Although this invention has been described in connection with specificforms and embodiments thereof, it will be appreciated that variousmodifications other than those discussed above may be resorted towithout departing from the spirit or scope of the invention. Forexample, equivalent elements may be substituted for those specificallyshown and described, certain features may be used independently of otherfeatures, and in certain cases, particular locations of elements may bereversed or interposed, all without departing from the spirit or scopeof the invention as defined in the appended Claims.

What is claimed is:
 1. An ambulatory patient monitoring system formeasuring and storing a plurality of electrocardiographic signals,comprising:a housing; a portable power supply disposed within saidhousing; microprocessor means disposed within said housing and beingcoupled to said portable power supply, said microprocessor having aplurality of operational speeds for (1) identifying a heart beat fromsaid electrocardiographic signals at one of said plurality ofoperational speeds, and (2) identifying and categorizing abnormalitiesin said electrocardiographic signals at another of said plurality ofoperational speeds for generating abnormality data; memory meansdisposed within said housing and coupled to said microprocessor meansfor storing said electrocardiographic signals and said abnormality data;variable clocking means disposed within said housing and coupled to saidmicroprocessor means for varying said plurality operational speedsthereof responsive to a signal from said microprocessor representing arespective one of (1) said identification of said heart beat, or (2)said storage of said electrocardiographic signals and said abnormalitydata to thereby conserve power from said portable power source; signalconditioning means disposed within said housing and coupled to saidmicroprocessor means for providing said electrocardiographic signalsthereto; and, lead means coupled to said signal conditioning means onend thereof for coupling said electrocardiographic signals from apatient to said signal conditioning means.
 2. The ambulatory patientmonitoring system as recited in claim 1 further comprising means formeasuring a predetermined physiological parameter of a patient disposedexternal said housing and coupled to said microprocessor means, saidmicroprocessor means further including means for generating a controlsignal responsive to said microprocessor means identifying apredetermined electrocardiographic abnormality for transmission of saidcontrol signal to said measurement means for triggering a measurement ofsaid physiological parameter responsive to said control signal.
 3. Theambulatory patient monitoring system as recited in claim 1 furthercomprising:a. means for measuring a predetermined physiologicalparameter of a patient disposed external said housing, said measuringmeans including (1) an optical input for receiving an optical signal,(2) measurement control means coupled to said optical input fortriggering a measurement of said physiological parameter responsive to areceived optical signal, and (3) an optical output coupled to saidmeasurement control means for serially transmitting data therefrom; and,b. an optical interface disposed within said housing and coupled to saidmicroprocessor means, said microprocessor means including means forgenerating a control signal responsive to said microprocessor meansidentifying a predetermined electrocardiographic abnormality, saidcontrol signal being optically transmitted from said optical interfaceto said optical input of said measuring means for triggering saidmeasurement of said physiological parameter responsive to said controlsignal.
 4. The ambulatory patient monitoring system as recited in claim3 where said optical interface includes:a. a plurality of light emittingdiodes; and; b. a plurality of tri-state drivers, each of said pluralityof tri-state drivers having (1) a power consuming on state, (2) a powerconsuming off state, and (3) a power saving high impedance state, eachof said tri-state drivers having an input coupled to said microprocessorand an output coupled to a respective one of said plurality of lightemitting diodes, each of said tri-state drivers having a control inputcoupled to said microprocessor for switching said tri-state drivers intosaid high impedance mode for disabling said respective light emittingdiodes.
 5. The ambulatory patient monitoring system as recited in claim4 where said optical interface further includes phototransistor meanshaving a pair of output terminals coupled to a respective pair of inputterminals of said microprocessor means for coupling respective signalsthereto responsive to receipt of said serial data transmitted from saidoptical output, said microprocessor means generating an interrupt signalresponsive to a first of said signals from said phototransistor meansresponsive to a first portion of said serial data from said opticaloutput for generating a ready-to-receive signal output from a particularone of said plurality of light emitting diodes, said microprocessormeans, receiving a second of said signals from said photoresistor meanssubsequent to said first signal, said second signal being defined by asecond portion of said serial data transmitted from said optical output.6. An ambulatory patient monitoring system for measuring and storing aplurality of electrocardiographic signals, comprising:a housing; aportable power supply disposed within said housing; microprocessor meansdisposed within said housing and coupled to said portable power supplyfor identifying and categorizing abnormalities in saidelectrocardiographic signals for generating abnormality data; memorymeans disposed within said housing and coupled to said microprocessormeans for storing said electrocardiographic signals and said abnormalitydata; signal conditioning means disposed with in said housing andcoupled to said microprocessor means for providing saidelectrocardiographic signals thereto, said signal conditioning meansincluding an adjustable gain amplifier coupled to said microprocessormeans for adjusting a gain value thereof responsive to a digital controlsignal generated by said microprocessor means by comparing an amplitudeof a detected R-wave of said electrocardiographic signals with apredetermined threshold value; and, lead means coupled to said signalconditioning means on one end thereof for coupling saidelectrocardiographic signals from a patient to said signal conditioningmeans.
 7. A method of monitoring the electrocardiographic signals of anambulatory patient, comprising the steps of:a. coupling at least a pairof electrodes to the ambulatory patient to conduct electrical signalstherefrom; b. amplifying said signals conducted from said electrodes bya gain value; c. filtering said amplified signals; d. providing asemiconductor memory and storing said filtered signals therein; e.selecting a threshold amplitude value; f. identifying an R-wave portionof said filtered signals and comparing an amplitude of said R-waveportion with said threshold amplitude value for increasing said gainvalue if said amplitude of said R-wave portion is less than saidthreshold amplitude value; g. measuring a timing value between eachsuccessive R-wave portions of said filtered signals; h. settingpredetermined limits for said timing value to identify predeterminedabnormal clinical conditions; i. classifying said timing valueresponsive to said timing value being outside said predetermined limitsfor identifying said predetermined abnormal clinical conditions; j.storing said identified clinical conditions in said semiconductormemory; k. preselecting a particular clinical condition; l. comparingsaid identified clinical conditions with said preselected clinicalcondition; m. providing means for output of a signal indicating at leastone of said identified clinical conditions being identical to saidpreselected clinical condition; n. measuring and classifying successivetiming values to identify heart rhythms; o. storing said identifiedheart rhythms in said semiconductor memory; p. providing means forreading and displaying data stored in said semiconductor memory, saiddata being defined by (1) said filtered signals, (2) said identifiedclinical conditions, and (3) said heart rhythms, said means for readingand displaying data including an optical interface coupled to saidsemiconductor memory; q. reading said data from said semiconductormemory through said optical interface; and, r. displaying said data readfrom said semiconductor memory.